One means of exposing photographic materials is a known image forming method using a so-called scanner system. An original is scanned and a silver halide photographic material is exposed on the basis of the resulting image signal so as to form a negative image or positive image corresponding to the image of the original thereon.
There are various practical recording devices which may be used in such a scanner system image forming method. The recording light sources for scanner system recording devices include a glow lamp, a xenon lamp, a mercury lamp, a tungsten lamp and a light emitting diode. However, all these light sources have the drawbacks that the output is weak and their life is short. To compensate for these drawbacks, there are known scanners which use coherent laser rays, such as a Ne--He laser, an argon laser or a He--Cd laser, as the light source for the scanning system. The coherent laser rays may yield a high output, but they have other drawbacks in that they need large-sized, high-priced devices and modulators. In addition, since visible rays are used, the safelight for the photographic materials is limited and the handlability of the devices is poor.
In contrast, devices for semiconductor lasers are small-sized and low-priced and may be easily modulated. In addition, semiconductor lasers have a longer life than the above-mentioned lasers. Moreover, since they emit infrared rays, a light safelight may be used in handling infrared-sensitive photographic materials. Therefore, semiconductor lasers are advantageous with respect to handlability and operability. Despite these advantages, since there are unknown excellent photographic materials having high infrared sensitivity and good storage stability, the excellent characteristics of these semiconductor lasers could not be utilized satisfactorily.
In one known technology for producing photographic materials, cyanine dyes of a certain kind are added to silver halide photographic materials so as to extend their light-sensitive range on the side of a longer wavelength. This is a so-called spectral sensitizing technology. It is also known that the spectral sensitizing technology may apply not only to rays of a visible range, but also to those of an infrared range. For infrared sensitization, sensitizing dyes capable of absorbing infrared rays are used, which are described in, for example, Mees, The Theory of the Photographic Process, 3rd Ed. (published by MacMillan, 1966), pages 198 to 201. In that case, the photographic materials desirably have a high sensitivity to infrared rays and a small variation in sensitivity, even during storage of the emulsions. For this purpose, various sensitizing dyes have heretofore been developed.
For instance, many sensitizing dyes are described in U.S. Pat. Nos. 2,095,854, 2,095,856, 2,955,939, 3,482,978, 3,552,974, 3,573,921 and 3,582,344. However, even though these sensitizing dyes are used, the sensitivity and storage stability of the photographic materials to which they are added could not be said to be fully sufficient.
On the other hand, it is also known that addition of a second specifically selected organic compound of a certain kind to the photographic materials, in addition to spectral sensitizing dyes, noticeably increases the spectral sensitivity of the materials; and the effect to be attained by the addition is known as a supersensitizing effect.
For supersensitization in the infrared range, JP-A-59-191032, JP-A-59-192242 and JP-A-60-80841 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describe the combination of infrared sensitizing dyes (tricarbocyanine dyes, 4-quinolinedicarbocyanine dyes) and cyclic onium salt compounds or heterocyclic compounds of certain kinds. However, the techniques as described in these publications are still insufficient for obtaining a sufficiently high sensitivity.
Since laser rays, including semiconductor laser rays, each have a determined wavelength, the photographic materials to be exposed to such laser rays typically will be selected so as to be only strongly sensitized by exposure to a particular ray having the same wavelength as the ray emitted by a laser. That is, in typical usages, the photographic materials are preferred which have a low sensitivity to any other rays in a wavelength range different from the wavelength of the ray to be emitted by a laser in view of the safelight safety concerns for the photographic materials. The technology of sensitizing photographic materials to only rays in a particular wave-length range is known as J-band sensitization in the field of spectral sensitization of silver halide photographic materials.
However, while many examples of J-band sensitization are known to visible rays, those known to infrared rays are scarce. Examples of the latter are mentioned in A. H. Henry, P.S.E. 18 (3), pp. 323-335 (1974), and H. Kampfer, ICPS Reports, pp. 366-369 (1986).
In an infrared-sensitized system having a sensitized peak in a wavelength region longer than 730 nm, when the amount of the dye to be added thereto is increased, the photographic material is strongly desensitized (e.g., see U.S. Pat. No. 4,011,083). Therefore, the dye-coated percentage of the surfaces of silver halide grains in the photographic material is generally restricted to approximately from 10 to 20%, but addition of the dye in such a limited amount could barely yield J-band sensitization.
Also, various organic compounds such as stabilizers are typically added to silver halide photographic materials, and various organic solvents such as methanol or ethanol are generally used as carriers for addition of such organic compounds. Where the organic solvent for this purpose is added in such a degree that it would not cause deterioration of the gelatin in the photographic material, there would occur no disadvantageous problems. However, where the photographic material is to be sensitized for J-band sensitization to rays being in a wavelength range longer than 730 nm, the presence of some organic solvents would cause noticeable hindrance and interfere with formation of J-band sensitization. Therefore, even though a photographic material is desired to be sensitized to rays being in a wavelength longer than 730 nm, J-band sensitization could not be attained if a conventional amount of a conventional dye is used along with a conventional amount of a conventional solvent.
Although the above-mentioned literature refers to J-band sensitization, the authors thereof did not have sufficient intention and knowledge of laser exposure and safe light handling of photographic materials, and, as a result, the authors' recognition of the importance of lowering the sensitivity of photographic materials to unnecessary rays was unsatisfactory. Under such situation, even though they succeeded in J-band sensitization, they could only obtain materials which were inadequate for practical use. In view of this situation, it has been desired in this field to develop a sensitization method capable of attaining J-band sensitization of photographic materials which are suitable for exposure to semiconductor laser rays while decreasing the undesired sensitivity of the photographic materials to other rays of different wavelength.
On the other hand, the speed of processing photographic materials with an automatic developing machine is being demanded to be increased more and more in current practice. With such increasing speed of processing, a sufficient time for decoloring the dye in the photographic materials being processed cannot be ensured so that the processed materials often have a problem caused by the residual color (i.e., remaining color) of dyes therein. Therefore, a sensitizing system causing little residual color in the processed photographic materials is desired.